This application claims the benefit of priority from Japanese Patent Application No. 2000-313445, filed on Oct. 13, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a liquid developer image forming apparatus, which forms an image on a substrate using a liquid developer containing toner particles and a solvent. The present invention also relates to an image forming method using the liquid developer.
2. Discussion of the Background
An image forming apparatus using a liquid developer has promising advantages over an image forming apparatus using dry toner. One advantage arises due to the fact that the liquid developer contains a carrier solvent and toner particles, which have an average particle size in the sub-micrometer range, much smaller than the size of dry toner particles, whereby high image quality is preferably obtained. The liquid developer also decreases the amount of toner particles needed to develop images, while maintaining high image density. Therefore, liquid toners are economical in addition to enabling realization of fine texture printed images. The liquid developer also allows fixing of a developed image onto a final substrate at relatively low temperature and therefore is preferable from the standpoint of energy conservation.
On the other hand, the image forming apparatus using liquid developer has several features, which have discouraged its use. One such feature is unpredictable instability of developing characteristic that may in dependence or selection of values result from each several operating parameters controlling the development.
Multicolor image can be formed on a photosensitive body by developing each color image on top of other color image(s) through an Image-On-Image (IOI) process and transferred to a substrate, for example a paper receptor. The IOI process does not need a large transfer drum which transfer the image from the photosensitive body to the final substrate but only one photosensitive body or a smaller transfer drum whereby a simple and compact multicolor developing apparatus can be realized. The apparatus using the IOI process is also preferable for improving alignment between color images and high speed of the image forming because of easy image transfer to the final substrate.
Several image forming apparatuses using the dry toner through the IOI process have been researched and produced (See The Transactions of the Institute of Electronics, Information and Communication Engineers J67-C(12), p.970(1984); Journal of the Imaging Society of Japan 26(2), p.107(1987); and Japan Hardcopy 89 p.163(1989)). However, those apparatuses had several essential problems to be resolved before realizing high quality of texture.
A first problem is that the dry toner layer on the photosensitive body may be so bulky as to scatter and absorb modulated light beams thereby bringing about poor light attenuation and uneven electric potential at charging and exposing steps for a next color image, thereby resulting in deterioration of quality. A second problem is that the previously formed image on the photosensitive body may be deteriorated and removed by the development of the next color image, so as to require non-contact developing with several restrictions on the developing condition. A third problem is that electrophoresis transfer cannot easily transfer at one time the multicolor image, which is exposed to corona ions and high efficiency and high quality of texture cannot be realized.
A liquid developer apparatus using the IOI process is also described in U.S. Pat. Nos. 4,660,503 and 5,557,377, however, no guidance for realizing stable high quality development is provided. Therefore a liquid developer image forming apparatus using the IOI process has not been known for practical use.
In various aspects, embodiments of the present invention provide image forming apparatuses and image forming methods which form an image on a substrate by using a liquid developer containing toner particles and a solvent.
According to a first aspect, one embodiment of the present invention provides a liquid developer image forming apparatus including a latent image retaining body, a first developing surface, a latent image forming unit, and a second developing surface. The latent image retaining body has a photosensitive layer having a relative dielectric constant ∈p [C2/Nm2] and an average thickness dp [m] and on which a latent image can be formed. The first developing surface faces the latent image retaining body at a first development station, and is supplied with an electrical potential for a first development. The first developing surface is configured to provide the first liquid developer to the latent image retaining body. The latent image forming unit also faces the latent image retaining body and is configured to form a second latent image comprising image and non-image regions on the photosensitive layer. The second developing surface also faces the latent image retaining body at a second development station and is supplied with an electrical potential for a second development which has an electrical potential difference xcex94V from an electrical potential of the non-image region of the second latent image. The second developing surface is configured to provide the second liquid developer to the latent image retaining body, and the latent image retaining body supports the image of the first liquid developer and the second latent image. The plurality of toner particles of the first liquid developer at the second development station have a volume density of toner particles xcfx81m [kg/m3], a surface density mr [kg/m2], a relative dielectric constant ∈r [C2/Nm2], an average radius r [m], and a density of electrical charge qr [C/kg] at the second development station. The first liquid developer image has an average thickness dr [m] at the second development station and the second liquid developer has an average thickness dt [m] at the second development station, and a relative dielectric constant ∈t [C2/Nm2]; and the parameters satisfy following equations,             1      xc3x97                        10                      -            11                          ⁡                  [          N          ]                      ≤                            4          ⁢          π          ⁢                      xe2x80x83                    ⁢                      r            3                    ⁢                      ρ            m                    ⁢                      q            r                          3            ⁢              (                              -                                                            q                  r                                ⁢                                  m                  r                                                                              ϵ                  r                                ⁢                                  d                  r                                                              ⁢                      (                                          d                r                            -                                                1                  A                                ⁢                                                      d                    r                                                        m                    r                                                  ⁢                                  (                                                            -                                                                        Δ                          ⁢                                                      xe2x80x83                                                    ⁢                          V                                                                          q                          r                                                                                      +                                                                  (                                                                                                            d                              r                                                                                      2                              ⁢                                                              xe2x80x83                                                            ⁢                                                              ϵ                                r                                                                                                              +                                                                                    d                              t                                                                                      ϵ                              t                                                                                                      )                                            ⁢                                              m                        r                                                                              )                                                      )                          )              ≤          8      xc3x97                        10                      -            9                          ⁡                  [          N          ]                      ,      
    ⁢            and      ⁢              xe2x80x83            ⁢      A        =                            d          p                          ϵ          p                    +                        d          r                          ϵ          r                    +                                    d            t                                ϵ            t                          .            
According to a second aspect, one embodiment of the present invention provides a liquid developer image forming apparatus comprising a latent image retaining body, a developing surface, and a squeezing surface. The latent image retaining body comprises a photosensitive layer configured to keep a latent image and having a relative dielectric constant ∈p [C2/Nm2], and an average thickness dp [m]. The developing surface faces the latent image retaining body at a development station and is supplied with an electrical development potential. The developing surface is configured to provide the liquid developer to the latent image retaining body which supports the photosensitive layer on which is formed a latent image including image and non-image regions. The squeezing surface also faces the latent image retaining body at a squeezing station and is supplied with an electrical potential producing an electrical potential difference xcex94V1 [V] relative to the electrical potential of the non-image region of the photosensitive layer. The latent image retaining body supports an image of the liquid developer and the plurality of toner particles of the image having a relative dielectric constant ∈0r, [C2/Nm2], an average radius r [m], a density of electrical charge q0r [C/kg], a volume density of toner particles xcfx810m[kg/m3], and a surface density m0r, [kg/m2]. The image at the squeezing station has an average thickness d0r, [m] and the liquid developer has an average thickness dt [m] at the squeezing station, and a relative dielectric constant ∈t [C2/Nm2]. The parameters satisfy following equations,                     6        xc3x97                              10                          -              11                                ⁡                      [            N            ]                              ≤                                    4            ⁢            π            ⁢                          xe2x80x83                        ⁢                          r              3                        ⁢                          ρ                              0                ⁢                m                                      ⁢                          q                              0                ⁢                r                                              3                ⁢                  (                                    -                                                                    q                                          0                      ⁢                      r                                                        ⁢                                      m                                          0                      ⁢                      r                                                                                                            ϵ                                          0                      ⁢                      r                                                        ⁢                                      d                                          0                      ⁢                      r                                                                                            ⁢                          (                                                d                                      0                    ⁢                    r                                                  -                                                      1                    A                                    ⁢                                                            d                                              0                        ⁢                        r                                                                                    m                                              0                        ⁢                        r                                                                              ⁢                                      (                                                                  -                                                                              Δ                            ⁢                                                          xe2x80x83                                                        ⁢                            V                                                                                q                                                          0                              ⁢                              r                                                                                                                          +                                                                        (                                                                                                                    d                                                                  0                                  ⁢                                  r                                                                                                                            2                                ⁢                                                                  xe2x80x83                                                                ⁢                                                                  ϵ                                                                      0                                    ⁢                                    r                                                                                                                                                        +                                                                                          d                                t                                                                                            ϵ                                t                                                                                                              )                                                ⁢                                                  m                                                      0                            ⁢                            r                                                                                                                )                                                              )                                )                    ≤              3        xc3x97                              10                          -              9                                ⁡                      [            N            ]                                ,          
        ⁢          xe2x80x83        ⁢    and        A    =                            d          p                          ϵ          p                    +                        d                      0            ⁢            r                                    ϵ                      0            ⁢            r                              +                                    d            t                                ϵ            t                          .            
According to a third aspect, one embodiment of the present invention provides an image forming method comprising steps of providing a first liquid developer at a first development station on a latent image retaining body which has a photosensitive layer, forming a second latent image on the photosensitive layer, and providing a second liquid developer on the latent image retaining body at a second development station using a development surface. The first liquid developer comprises a solvent and a plurality of toner particles. The photosensitive layer retains an image of first liquid developer and a non-image region. The photosensitive layer has a relative dielectric constant ∈p [C2/Nm2] and an average thickness dp [m]. The second latent image has an image region and a non-image region. The toner particles of the image of first liquid developer at the second development station has a volume density xcfx81m [kg/m3], a relative dielectric constant ∈r [C2/Nm2], an average radius r[m], a density of electric charge qr [C/kg], and a surface density mr [kg/m2]. The first image of the first liquid developer on the photosensitive layer has an average thickness dr [m], and the electrical potential of the non-image region of the second latent image has an electrical potential difference xcex94V [V] relative to the electrical potential of the development surface. The second liquid developer has an average thickness dt [m] at the second development station and a relative dielectric constant ∈t [C2/Nm2]. Those parameters satisfy following equations.             1      xc3x97                        10                      -            11                          ⁡                  [          N          ]                      ≤                            4          ⁢          π          ⁢                      xe2x80x83                    ⁢                      r            3                    ⁢                      ρ            m                    ⁢                      q            r                          3            ⁢              (                              -                                                            q                  r                                ⁢                                  m                  r                                                                              ϵ                  r                                ⁢                                  d                  r                                                              ⁢                      (                                          d                r                            -                                                1                  A                                ⁢                                                      d                    r                                                        m                    r                                                  ⁢                                  (                                                            -                                                                        Δ                          ⁢                                                      xe2x80x83                                                    ⁢                          V                                                                          q                          r                                                                                      +                                                                  (                                                                                                            d                              r                                                                                      2                              ⁢                                                              xe2x80x83                                                            ⁢                                                              ϵ                                r                                                                                                              +                                                                                    d                              t                                                                                      ϵ                              t                                                                                                      )                                            ⁢                                              m                        r                                                                              )                                                      )                          )              ≤          8      xc3x97                        10                      -            9                          ⁡                  [          N          ]                      ,      
    ⁢            and      ⁢              xe2x80x83            ⁢      A        =                            d          p                          ϵ          p                    +                        d          r                          ϵ          r                    +                                    d            t                                ϵ            t                          .            
According to a fourth aspect, one embodiment of the present invention provides an image method comprising steps of developing a latent image of a photosensitive layer with a liquid developer containing a solvent and a plurality of toner particles, and squeezing the solvent formed on the latent image retaining body by using a squeezing surface at a squeezing station. The photosensitive layer is configured to keep a latent image and has a relative dielectric constant ∈p [C2/Nm2] and an average thickness dp [m]. The squeezing surface is supplied with a squeezing electrical potential having an electrical potential difference xcex94V1 [V] relative to an electrical potential of the non-image region of the photosensitive layer and the plurality of toner particles of the image have a relative dielectric constant ∈0r [C2/Nm2], an average radius r [m], a density of electrical charge q0r [C/kg], a volume density of toner particles xcfx810m [kg/m3], and a surface density m0r [kg/m2]. The image at the squeezing station has an average thickness d0r [m] at the squeezing station, and the liquid developer has an average thickness dt [m] at the squeezing region, and a relative dielectric constant ∈t [C2/Nm2]. The parameters satisfy following equations,             6      xc3x97                        10                      -            11                          ⁡                  [          N          ]                      ≤                            4          ⁢          π          ⁢                      xe2x80x83                    ⁢                      r            3                    ⁢                      ρ                          0              ⁢              m                                ⁢                      q                          0              ⁢              r                                      3            ⁢              xe2x80x83            ⁢              (                              -                                                            q                                      0                    ⁢                    r                                                  ⁢                                  m                                      0                    ⁢                    r                                                                                                ϵ                                      0                    ⁢                    r                                                  ⁢                                  d                                      0                    ⁢                    r                                                                                ⁢                      (                                          d                                  0                  ⁢                  r                                            -                                                1                  A                                ⁢                                                      d                                          0                      ⁢                      r                                                                            m                                          0                      ⁢                      r                                                                      ⁢                                  (                                                            -                                                                        Δ                          ⁢                                                      xe2x80x83                                                    ⁢                          V                                                                          q                                                      0                            ⁢                            r                                                                                                                +                                                                  (                                                                                                            d                                                              0                                ⁢                                r                                                                                                                    2                              ⁢                                                              xe2x80x83                                                            ⁢                                                              ϵ                                                                  0                                  ⁢                                  r                                                                                                                                              +                                                                                    d                              t                                                                                      ϵ                              t                                                                                                      )                                            ⁢                                              m                                                  0                          ⁢                          r                                                                                                      )                                                      )                          )              ≤          3      xc3x97                        10                      -            9                          ⁡                  [          N          ]                      ,      
    ⁢            and      ⁢              xe2x80x83            ⁢      A        =                            d          p                          ϵ          p                    +                        d                      0            ⁢            r                                    ϵ                      0            ⁢            r                              +                                    d            t                                ϵ            t                          .            